Rarotonga is the largest (64 km2
) and by far the highest (652 m)
of the Cook Islands. The native coastal and lowland vegetation of this high
volcanic, tropical island has been either completely removed or heavily disturbed.
Numerous exotic plant species have been introduced and many of these are now
naturalized in the lower elevation habitats of the island. The results of this initial,
quantitative study in the upland forests of Rarotonga indicate, however, that the
plant life of the rugged interior is still largely dominated by native species. Over
92 percent of all the woody plants (dbh > 2.5 cm) sampled in the 19 upland
forest transects are either indigenous or endemic to Rarotonga. Native plants
also accounted for more than 95 percent of the basal area covered by the woody
vegetation in the upland study area. Three basic native plant associations have
been recognized by dendrogram analysis: (1) the Homalium montane forest; (2)
the Fagraea-Fitchia ridge forest; and (3) the Metrosideros cloud forest. The first
two associations develop under subtropical climatic conditions, while the cloud
forest is adapted to warm temperate conditions. Some aspects of the biogeographical
significance of this unique forest region and the ecological implications
of human disturbance in the uplands are also discussed.